Dresden 2014 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 57: Transport: Molecular Electronics I
TT 57.8: Talk
Wednesday, April 2, 2014, 11:45–12:00, HSZ 304
Kondo-effect in binuclear metal-organic molecules — •Dimitra Xenioti1,2, Alexej Bagrets1, Richard Korytár1, Lei Zhang1,3, Frank Schramm1, Mébarek Alouani2, Mario Ruben1,2, Wulf Wulfhekel1,3, and Ferdinand Evers1,4 — 1Institute of Nanotechnology (INT), KIT, Karlsruhe, Germany — 2Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Strasbourg, France — 3Physikalisches Institut (PI), KIT, Karlsruhe, Germany — 4Institut für Theorie der Kondensierten Materie (TKM), Karlsruhe, Germany
Low-temperature STM measurements performed on a binuclear metal-organic molecule (Ni(hfacac)2)2(bpmd) ("Ni2") deposited on a Cu surface reveal that the system undergoes a Kondo effect with TK ∼ 10K and a spin located nearby Ni atoms. The physics in play is intriguing, because the molecule does not have anchoring groups, which could be responsible for the formation of a chemical bond with the Cu surface. By comparing experimental data with simulated STM images, we have identified possible adsorption geometries. Our simulations show that some observed STM images and large TK could be attributed to a distorted "Ni2" complex, which is bound to Cu(001) via the bipyrimidine (bpmd) unit. Other images may be interpreted as arising from molecular fragmentation, suggesting a Ni(hfacac)2 moiety to be seen in the experiment. In the latter case our analysis of the DFT+U (Kohn-Sham) spectral function show that the S=1 type Kondo effect arises mainly due to unpaired electrons populating dxy and dz2 orbitals of Ni2+ ion. In the case of "Ni2", our calculations suggest that the Kondo effect originates from a pair of weakly coupled S=1 Ni2+ spins.